There has been considerable interest in using rare earth doped fiber amplifiers to amplify optical signals used in communications networks. The rare earth doped fiber amplifiers are found to have low cost, exhibit low-noise, provide relatively large bandwidth which is not polarization dependent, display substantially reduced crosstalk, and present low insertion losses at relevant operating wavelengths. As a result of their favorable characteristics, rare earth doped fiber amplifiers, i.e., erbium-doped fiber amplifiers (EDFA's) are replacing current optoelectronic regenerators in many optical lightwave communications systems, and particularly, wavelength-division-mulltiplexed (WDM) optical communications systems.
A known characteristic of EDFA's is that the gain of an EDFA is not flat over a wide range WDM bandwidth. As such, the number of channels in fiber communications systems employing EDFA's is limited. The prior art has solved this problem by adding gain equalization filters (GEF's) in the EDFA's. Unfortunately however, the correct design of a particular GEF is often difficult to produce analytically or numerically. In particular, numerical simulation methods are oftentimes inaccurate, resulting in part from errors in EDF parameters, component loss estimation, and spectral hole burning. Consequently, a continuing need exists for methods and apparatus that facilitate the design of GEF's used in fiber communications systems.